1. Field of the Invention
The present invention relates generally to an improved interbody (for placement at least in part between adjacent vertebral bodies) threaded spinal fusion implant for the immobilization of vertebrae. The present invention is directed to threaded implants only and not to non-threaded implants. In particular, the invention relates to a threaded spinal fusion implant that is selectively directionally expandable and which specifically has height raising capabilities that are utilized once the implant is initially positioned. More particularly, the invention relates to a threaded implant having arcuate portions of upper and lower members that in a first, collapsed, or insertion position are angled to one another and form at least a portion of a frusto-conical shape along a substantial portion of the length of the implant.
2. Description of the Related Art
Threaded spinal fusion implants are known in the related art. The first artificial threaded spinal fusion implant was invented by Michelson and is disclosed in U.S. Pat. No. 5,015,247, which is hereby incorporated by reference.
Lordotic, frusto-conical, or tapered, threaded-spinal fusion implants are also known in the art. By way of example, Michelson has invented such implants as disclosed in U.S. application Ser. No. 08/480,904, which is hereby incorporated by reference.
Expandable fusion implants are known in the related art. The first expandable spinal fusion (allowing for the growth of bone from vertebral body to vertebral body through the implant) implant was invented by Michelson and is disclosed in U.S. Pat. No. 5,776,199, which is hereby incorporated by reference.
Lordotic, frusto-conical, or tapered, spinal fusion implants have the advantage of restoring or enhancing spinal lordosis. Threaded spinal fusion implants offer the advantage of being easily positioned in the implantation space and of having excellent fastening or holding features. Expandable fusion implants offer the advantage of allowing for the placement of a potentially larger implant through a smaller opening in a patient's body. Selective expansion along a single direction, (e.g. vertical only when correctly installed) offers the advantage of increasing the height of the implant and therefore the distraction of the disc space, but without a concomitant increase in the width of the implant.
There exists a need for an artificial interbody spinal fusion implant providing for all of the aforementioned advantages in combination.